It is well known in electronic systems for a common resource, such as a memory system, to be utilized by a number of individual system elements or subsystems. Such sharing of a common resource necessarily requires that each subsystem utilizing the common resource be given a usage priority. In addition, in many systems, it is often required that one of the plurality of subsystems be given priority over the remaining subsystems or alternatively that one subsystem have a faster access time than the remaining subsystems.
In order to accomplish the required delegation of usage priorities it is necessary to utilize apparatus to arbitrate between the various usage requests. Prior art arbitration apparatus suffers from several disadvantages. One of these is that much of the prior art arbitration apparatus is unduly complex and expensive. Another disadvantage in the prior art is the inability of the prior art apparatus to grant priority to one of a plurality of requests notwithstanding the fact that the one request is detected subsequent to one or more of the remaining requests. Finally, much of the prior art arbitration apparatus suffers from the electrical noise problem wherein when two or more requests arrive at substantially the same time the apparatus often generates an unwanted voltage transient which can cause circuit malfunction.
It is therefore, an object of this invention to provide arbitration apparatus which is simple and inexpensive.
It is another object of this invention to provide arbitration apparatus which can grant priority to one of a plurality of requests notwithstanding the fact that the one request is detected subsequent to the remaining requests, while providing faster access time to another one of the plurality of requests.
It is a further object of this invention to provide arbitration apparatus which solves the "glitch" problem inherent in the prior art.